The Vegetation Classification developed
for the Napa County MCV map
(Includes only Alliances found on the Quail Ridge
Thorne, J. H., J. A. Kennedy, J. F. Quinn, M. McCoy,
T. Keeler-Wolf and J. Menke.
(Made possible by funding from the California Department
the David and Lucille Packard Foundation, and the National Fish
and Wildlife Foundation)
Napa County Mapping Classification
The National Vegetation Classification System (NVCS)
establishes a hierarchy for vegetation cover types, with the Class,
Subclass, Group and Formation levels forming the highest (coarsest)
levels of the hierarchy, based on the physiognomy of the vegetation.
The Alliance and the Association form the lowest (finest) levels
of the hierarchy, and are based on floristic composition within
a given physiognomic Formation. The Manual of California Vegetation
(MCV) is the local implementation of the NVCS for California.
For mapping purposes, individual Alliances often
cannot be distinguished on the base map imagery, but multiple aggregations
of Alliances within a given Formation can be distinguished and mapped.
The same is true at the Association level. Rather than lose vegetative
resolution by mapping to the next coarsest level in the hierarchy
(i.e., the Formation or the Alliance level, respectively) mappers
will resort to ad hoc cover types of aggregated Alliances, here
called Super Alliances, or aggregated Associations, here called
Super Associations. When new plot data collection is not an integral
component of the mapping project, as was the case for this first
edition of the Napa vegetation map, these provisional cover types
are not formally defined by quantitative cover data. In the classification
below, these provisional types are preceded by NFD, for “not
formally defined.” The authors are currently seeking funding
for the field-based data collection needed to revise the classification
and define these provisional types.
In the NVCS, each entry in the hierarchy has a
unique alphanumeric code. These NVCS codes are long and unwieldy
for map display of individual polygon (stand) labels. In current
mapping practice, short four-digit codes are used instead. These
have the advantage of compactness, but the disadvantage of being
unique only to the particular map in question. The same numeric
code could stand for a different cover type on a different map.
They are merely codes of convenience for map labeling purposes.
Note, also, that while codes in the even thousands refer to Class
- Subclass entities and those in the even hundreds refer to Group
- Formation entities, those with non-zero digits in the tens and
ones place can refer to entities at either the Super Alliance, Alliance,
Super Association or the Association level. The level of indentation
provides a visual clue as to the appropriate hierarchical level
for a given cover type. Note that cover types at the Super Association
or Association level may occur out of strict numerical sequence.
MCV Vegetation Mapping Hierarchy
Class - Subclass (Level 1)
Group - Formation (Level 2)
Super Alliance - Alliance (Level 3)
Super Association - Association (Level 4)
NOTE: Types in bold face are discernible
on the digital orthophoto quarter quad (DOQQ) black and white base
map imagery or can be correlated to environments and have been mapped
in the county. All hierarchical levels are shown for context. Physignomic
Formations shown in boldface (n = 3) represent mapped cover types,
usually for post-disturbance stands that are too early in their
successional sequence to reliably map at a finer level. At the time
the mapping project began, the most recent DOQQs dated from 1993.
Napa County flew color imagery for DOQQ production in late April
2002. The resulting color DOQQs should be available in early 2004
for the entire county and will be used for map revision.
1200 - Xeromorphic Sclerophyll Woodlands
1222 – Interior Live Oak Alliance
Quercus wislizeni is uncommon as a
sole component to a hardwood canopy. This cover type is generally
found on steep northerly slopes in closed stands in the eastern
portions of the county that may contain a minor component of
Q. douglasii and/or Pinus sabiniana and often
transitions to a mesic chaparral containing scrub Q. wislizeni
ssp. frutescens, Umbellularia californica, Q. berberidifolia,
Cercocarpus betuloides and Fraxinus dipetala.
It is mapped only east of Lake Berryessa on north trending slopes.
1223 – Mixed Oak Alliance
Very common throughout the county, this type
is mapped as several different provisional associations where
at least two or more oaks, discernable on the DOQQ base map
imagery, co-dominate. Lowest elevations often contain a mix
of Quercus agrifolia and Q. lobata. Q.
garryana may be a component to this phase, especially north
of Napa. Higher elevations will always have a significant component
of Q. kelloggii, with Q. chrysolepis playing
an important role in steeper settings. Other hardwoods often
occur in the stand as a minor component, with Acer macrophyllum
occurring in more mesic settings, and Arbutus menziesii
in more xeric sites. At higher elevations in open woodland settings,
Q. kelloggii and Q. douglasii may occasionally
mix. Conifers, especially Pinus ponderosa or Pseudotsuga
menzeisii, may occur as a minor component to higher elevation
stands generally below 10% relative cover.
1202 – Interior Live Oak - Blue Oak - (Foothill
Pine) NFD Association
This is a common type that generally replaces
type 1201 east of the Napa River watershed. This type is a
provisional association of the Mixed Oak Alliance (1223) that
can be reliably identified and mapped on the b&w DOQQs
base maps. It is found in somewhat steeper settings than the
Blue Oak Alliance (3122). Both oak species contain at least
10-15% relative cover. Pinus sabiana is often a co-dominant
but with generally less than 15% relative cover.
2000 – Evergreen Needle-leaf Forests &
2100 – Rounded Crown Forests & Woodlands
(Pines & Cypress)
2104 – Foothill Pine / Mesic Non-serpentine Chaparral
Several stands were noted in the eastern portion
of the county, where Pinus sabiniana is emergent to
non-serpentine chaparral or scrubby Umbellularia californica.
3000 – Deciduous Forests & Woodlands
3100 – Cold Season Deciduous Forests & Woodlands
3121 – Black Oak Alliance
This type occurs at higher elevations, especially
in the Atlas Peak region, on gentle to moderate slopes trending
in most directions except south. Outside of this type, Quercus
kelloggii is generally mapped as a component to the mixed
oak mapping unit.
3122 – Blue Oak Alliance
This type occurs occasionally on slopes just
east of the Napa Valley, and extensively east of Chiles Valley
to the Yolo County line. Stands vary from nearly closed to very
open, where Quercus douglasii makes up at least 80-90%
relative cover. The most common associate is Q. wislizeni,
but other oaks may be a minor component, especially at higher
elevations or in west county stands.
3123 – Valley Oak Alliance
This type is fairly common, especially in the southern portion
of the county, on gentle to nearly level slopes in open settings.
It is generally mapped where Quercus lobata is the
primary dominant species. It mixes most often with Q. agrifolia.
This type occurs occasionally on slopes just east of the Napa
Valley, and extensively east of Chiles Valley to the Yolo County
line. Stands vary from nearly closed to very open, where Quercus
douglasii makes up at least 80-90% relative cover. The
most common associate is Q. wislizenii, but other oaks
may be a minor component, especially at higher elevations or
in west county.
SHRUBLAND - DWARF SHRUBLAND
4000 – Evergreen Shrubland
4300 – Sclerophyllous Shrubland Formation
Mapped in disturbed settings and post fire stands, generally
less than 15 years old.
4301 – Scrub Interior Live Oak - Scrub Oak -
(California Bay - California Ash - Birch Leaf Mountain Mahogany
- Toyon - California Buckeye) Mesic East County NFD Super Alliance
This type occurs in dense stands, especially
along the crest of the Blue Ridge, often associated with the
Interior Live Oak (Forest) Alliance (1222), which occurs in
slightly more mesic settings.
4321 – Chamise Alliance
Mapped frequently throughout the county on
xeric slopes where Adenostoma fasciculatum makes up
at least 70-80% relative cover, generally in a closed chaparral
4322 – Chamise - Wedgeleaf Ceanothus Alliance
Chamise and wedgeleaf ceanothus important shrubs
in canopy; black sage, California buckwheat, chaparral yucca,
manzanitas, and/or scrub oak may be present. Shrubs < 3 m;
canopy continuous. Ground layer sparse or absent.
6000 – Perennial Herbaceous (Graminoid - Forbs)
6400 – Semi permanently - Permanently flooded Grasslands
6402 – (Bulrush - Cattail) Fresh Water Marsh
NFD Super Alliance
Most mappable stands are found along edges of small ponds and
reservoirs. It is a Super Alliance, because the separate Bulrush
and Cattail Alliances can’t be distinguished on the base
DOQQ imagery and may co-occur.
7000 – Annual Herbaceous (Graminoid - Forbs)
7100 – Upland Annual Grasslands & Forbs Formation
Generally mapped in stands that are somewhat more disturbed and
contain a higher non-native forb component than type 7120. Also
mapped in ruderal settings south of the town of Napa.
7120 – California Annual Grasslands Alliance
Mapped in settings where trees make up less
than 5-10% emergent cover in fairly natural settings that have
not been recently cleared.
Photo Credits: Title, Shooting Stars (Karen Mabry)